/Engine/Plugins/FX/Niagara/Source/Niagara/Public/NiagaraParameterStore.h
Gets the index of the passed parameter. If it is a data interface, this is an offset into the data interface table, otherwise a byte offset into the parameter data buffer.
int32 IndexOf ( const [FNiagaraVariableBase](API\Plugins\Niagara\FNiagaraVariableBase) & Parameter ) const